This invention relates to treatment of gaseous waste containing sulfur, or nitrogen compounds and more particularly relates to biological treatment systems for such gaseous waste.
It has been known that retention ponds could be built for holding aqueous waste materials containing undesirable materials and that to some extent such materials could be biologically metabolized and degraded by organisms within the pond. Such ponds have, however, been difficult to manage in that the undesirable materials (pollutants ) could overwhelm many desirable life forms within the pond thus causing it to become biologically unstable. Additionally, metabolic products build up which are toxic to the metabolizing organisms. Removal of such toxic products was difficult and expensive and sometimes not even possible. Furthermore, to maintain a viable population of such organisms, nutrients often had to be supplied to the pond, especially when commonly occurring organisms were depleted or destroyed by toxic pollutants or metabolic products.
It has further been known to use bacteria as the organisms for metabolizing the undesirable waste materials. For example bacteria of the genus Thiobacillus is known to convert certain undesirable liquid and gaseous sulfur containing compounds such as hydrogen sulfide, mercaptans, inorganic sulfides, sulfites and carbon disulfide into more biologically inert metabolic by-product compounds containing SO.sub.4.sup.=. Unfortunately, most such SO.sub.4.sup.= containing compounds are usually in the form of sulfuric acid which rapidly becomes toxic and must be neutralizer. Examples of such Thiobacillus bacteria include Thiobacillus thiooxidans, Thiobacillus ferrooxidans, Thiobacillus thioparus, Thiobacillus denitrificans, Thiobacillus neapolitanus, Thiobacillus tepidarius, Thiobacillus versutus and Thiobacillus intermedius. The bacteria Thiobacillus denitrificans is also known to metabolize undesirable nitrogen containing compounds.
Other bacteria are known which will metabolize alcohols, such as methanol and ethanol, methane, ketones, aldehydes, esters, ethers and carboxylic acids such as acetic and formic acids.
It has also been known to attempt to neutralize metabolically produced acids by throwing lime or ground limestone into a pond. Such an approach is messy, expensive and poses other problems associated with turbidity and floating of powdered material and usually does very little to offset the toxic effects of introduced pollutants.
Attempts have been made to biologically treat aqueous not gaseous effluents within columns containing limestone for purposes of neutralization. Nutrients must be added to and maintained within the waste stream in proper concentration which is exceedingly difficult. When undesirable microbial colonies become established they can overpower desirable organisms or shield the limestone from contact with acid within water passing through the column. When desirable microorganisms are replaced by other undesirable organisms or killed by improper nutrient balance or when the limestone must be replaced, desirable colonies must again be reestablished. This is often time consuming and difficult.